In an electrophotographic image forming process, visible images are formed is such a way that an electrostatic latent image member consisting of a photoconductive material is charged with electricity; an electrostatic latent image is formed on the charged electrostatic latent image member by exposure to a light pattern; a toner containing a colorant is applied on to the electrostatic latent image to form a toner image; the toner image is transferred to a transfer medium such as paper; and the transferred toner image is fixed to form a visible image.
As a toner for development of electrostatic images, a pulverized toner, a polymerized toner and others are known. A pulverized toner, which uses pulverized particles having sizes of about from 1 to 10 μm, is obtained by dispersing a colorant (such as carbon black, dye and pigment) in a binder resin (such as polystyrene) and pulverizing thus-obtained dispersed resin. To prepare a polymerized toner, a colorant is dispersed or dissolved in a polymerizable monomer to obtain a monomer composition, and the monomer composition is emulsified or suspended in an aqueous dispersion medium, polymerized, and agglomerated if necessary.
In an electrophotographic image forming process, use of a color process is becoming more popular and more advanced, and color toners which correspond to color-image forming apparatuses are increasingly demanded. It is known that a color-image forming apparatus is equipped with several image forming installments and each image forming installment forms a toner image in one color which is different in color from images formed by other installments. Toner images thus made in colors such as yellow, magenta, cyan and black are superimposed onto the single recording medium one by one.
Irrespective of a pulverized toner or a polymerized toner to be used, the following is required for a color toner:    (1) High transparency to enable superimposition of multiple colors.    (2) Excellent spectral reflection to enable reproduction of colors.    (3) Precise control of positive or negative charge level.    (4) Low fixing temperature.    (5) Easy manufacturing of color toners.
Conventionally, various techniques have been proposed to cope with above-described requirements. For example, Japanese Patent Application Laid-Open No. 1986-149969 has proposed that an additive for improving charge level, which is a polymer of amine group-containing monomer, is mixed with a pigment in halogenated hydrocarbon solvent such as chloroform using roll-mill. Then, the solvent is evaporated to form a pigment, to whose surface the additive for improving charge level is adhered. Thereafter, the pigment and resin particles are mixed by melting and pulverized to form a toner composition. Japanese Patent Application Laid-Open No. 1987-119549 has disclosed a toner production process in which a binder resin is dissolved in a solvent, and a colorant and a charge controlling agent are added thereto, and then they are mixed by agitation, thereafter the solvent is removed by freeze-drying. The resulting toner is pulverized and classified. Japanese Patent Application Laid-Open No. 1991-155568 has disclosed a toner production process in which a binder resin, at lease one of dye or pigment, and a solvent are mixed and mixed to form a masterbatch of the dye or pigment, and then the resulting masterbatch is further mixed with a binder resin and other additives if necessary; thereafter, they are pulverized and classified. Japanese Patent Application Laid-Open No. 1992-242752 has disclosed a color toner and a production process thereof, where a color toner is produced in a manner that a pigment dispersed in a binder resin, which is prepared by heating a pigment in a binder resin and mixing the mixture thereof, is further mixed with a binder resin; the resulting mixture are melted, mixed and classified to prepare a color toner; said color toner has at most 0.1% proportion of number of particles having at least 0.3 μm in diameter (presuming a circle for a particle) existing in a binder.
However, even with those proposals, it is extremely difficult to satisfy spontaneously various requirements for color toners as stated above. Particularly, it is difficult to prepare a color toner which has stable charge level and is excellent in transparency and spectral reflection properties.